Phase shift mask fabrication method thereof and fabrication method of semiconductor apparatus

ABSTRACT

There is disclosed an extreme ultraviolet phase shift mask that may be constituted practically by obtaining an appropriate combination of a refractive index with an absorption coefficient, even in the case of a reflection of an extreme ultraviolet radiation. When constituting a phase shift mask ( 10 ) having a reflective mask blank with multilayered films ( 11 ) that reflects a short ultraviolet light and a first and a second regions ( 12   a ) and ( 12   b ) formed on the reflective mask blank with multilayered films ( 11 ), firstly, with reference to an arbitrary complex refractive index to the extreme ultraviolet radiation and an arbitrary thickness of a film, a phase and a reflectance of a reflected light contained in the extreme ultraviolet radiation based on the above complex refractive index and the above film thickness are specified. Then, each film thickness and each complex refractive index in formative films of the first and the second regions ( 12   a ) and ( 12   b ) are set based on the specific results of the phase and the reflectance to ensure that the reflected light contained in the exposure light in the first region ( 12   a ) and the reflected light contained in the exposure light in the second region ( 12   b ) create a prescribed phase difference.

TECHNICAL FIELD

The present invention relates to a phase shift mask for use in alithography process for forming a circuit pattern of a semiconductorapparatus, a fabrication method thereof, and a fabrication method of asemiconductor apparatus including the lithography process, and moreparticularly, to a phase shift mask adaptable to so-called extremeultraviolet radiation, a fabrication method thereof, and a fabricationmethod of a semiconductor apparatus.

BACKGROUND ART

In recent years, with a micro-miniaturization of a semiconductorapparatus, a minimization of a pattern width (a line width) and aninter-pattern pitch, etc. have been required for a circuit patternformed on a wafer and a resist pattern, etc. for forming the circuitpattern. Such requirement for the above minimization is satisfied byfurther shortening a wavelength of an ultraviolet light for use in anexposure of a resist. As the micro-miniaturization of the semiconductorapparatus has advanced, the ultraviolet light for use in the exposurehas also required a shorter wavelength such as to apply a wavelength of365 nm to a semiconductor apparatus of 350 nm in design rule, awavelength of 248 nm to semiconductor apparatuses of 250 nm, and 180 nmin design rule and a wavelength of 193 nm to semiconductor apparatusesof 130 nm and 100 nm in design rule, for instance, leading to a use ofan ultraviolet light having a further shorter wavelength down to 157 nm.

It is generally known that a resolution based on these wavelengths isexpressed with a Rayleigh's formula in terms of w=k1×(λ/NA), where w isa resolved pattern of a minimum width, NA is a numerical aperture of anoptical projection lens, and λ is a wavelength of an exposure light.Further, k1 is a process coefficient determined mainly depending on aresist performance and a selected resolution enhanced technology, etc.,and it is known that the use of an optimum resist and an optimumresolution enhanced technology enables a selection of k1 to an extent ofabout 0.35. Incidentally, the resolution enhanced technology is intendedto obtain a pattern smaller than a wavelength using selectively ± firstorder diffracted light contained in a light having been diffracted witha shielding pattern on a mask after a transmission through the mask.

According to the Rayleigh's formula, it may be appreciated that aminimum pattern width w adaptable to the use of the wavelength of 157nm, for instance, reaches 61 nm, provided that a lens having NA of 0.9is applied. That is, it is necessary to use an ultraviolet light havinga wavelength shorter than 157 nm to obtain a pattern width smaller than61 nm.

For the above reason, an examination has been made recently on the useof an ultraviolet light called an extreme ultraviolet (EUV: ExtremeUltra Violet) radiation having a wavelength of 13.5 nm as theultraviolet light having the shorter wavelength than 157 nm. However, alight-transmitting material such as CaF₂ (Calcium Fluoride) and SiO₂(Silicon Dioxide), for instance, is available for the ultraviolet lighthaving the wavelength down to 157 nm, so that it is possible tofabricate a mask and an optical system that configured to transmit theabove extreme ultraviolet radiation. On the contrary, as for the extremeultraviolet radiation having the wavelength of 13.5 nm, there is nomaterial that allows the above extreme ultraviolet radiation to betransmitted through a desired thickness. Thus, when the ultravioletlight having the wavelength of 13.5 nm is used, it is necessary toconfigure a mask and an optical system with a reflective mask and areflecting optical system that allow a reflection of the light, insteadof the light-transparent mask and the light-transmitting optical system.

The reflective mask when used requires that a light having beenreflected from a mask surface should be led to an optical projectionsystem without causing a mutual interference with a light incident onthe mask. Thus, the light incident on the mask becomes inevitablynecessary to be obliquely incident with an angle φ to a normal of themask surface. This angle is determined from the numerical aperture NA ofthe optical projection lens, a mask magnification m and a size σ of anillumination light source. Specifically, as for an exposure apparatusconditioned to be NA=0.3 and σ=0.8, the use of a mask having a five-foldreduced magnification on the wafer, for instance, results in anincidence of the light on the mask with a solid angle of 3.44±2.75°.Further, as for an exposure apparatus conditioned to be NA=0.25 andσ=0.7, the use of a mask having a four-fold reduced magnification on thewafer results in the incidence of the light on the mask with the solidangle of 3.58±2.51°. An incident angle of the exposure light incident onthe mask is set so as to be normally close to 5° in consideration ofthese solid angles. The incident angle is defined herein as an anglethat is formed with the normal to the mask surface.

When the extreme ultraviolet radiation having the wavelength of 13.5 nmis reflected with the above reflective mask, the exposure apparatusconditioned to be NA=0.25, for instance, makes it possible to form aline width of 32.4 nm, provided that k1 ≧0.6 is derived from the abovementioned Rayleigh's formula. That is, the use of the extremeultraviolet radiation and the reflective mask that enables a patterntransfer with the extreme ultraviolet radiation is supposed to beadaptable also to the pattern width or pattern pitch minimization, etc.that has failed to be attained with the light-transparent mask and thelight-transmitting optical system.

By the way, a demand for the micro-miniaturization has been rapidlyincreased in recent years, resulting in a need for a measure to meet afurther minimization of the pattern width and the pattern pitch, etc. Asfor a gate line width requiring a small size in particular, forinstance, there has been also the need for a line width of a sizesmaller than 32.4 nm, that is, a condition under which k1<0.6 isderived. Specifically, a gate line width of 15 nm resulting from afabrication leads to the need for a 25 nm line width also as for aresist line width. In terms of the resist line width of 25 nm, k1=0.46is derived from the Rayleigh's formula in the case of the exposureapparatus conditioned to be NA=0.25 with the wavelength of 13.5 nm. Incase of forming the line width of the above size, it is necessary to usenot only the extreme ultraviolet radiation having the wavelength of 13.5nm and the reflective mask that reflects this extreme ultravioletradiation but also the resolution enhanced technology.

It is known that the resolution enhanced technology makes use of, inaddition to (1) a modified illumination light source (an orbicular zonalillumination and a four-hole illumination etc.) and (2) a pupil filter(a orbicular zonal filter and a four-hole filter etc.) that selectivelytake advantage of ± primary diffracted light of a mask pattern, (3) ahalftone phase shift mask, (4) a combination of the halftone phase shiftmask with the modified illumination light source, or (5) a Levensonphase shift mask (which is also called “an alternating phase shiftmask”). Each of (3), (4), and (5) (the halftone phase shift mask and thealternating phase shift mask are hereinafter referred generally to as“the phase shift mask”) takes advantage of an optical phase difference,and is quite effective in enhancing a resolution performance and inincreasing a pattern contrast, leading to a more frequent use for thelithography process than (1) or (2).

However, while the transparent mask that is of a light transmitting typeis easy to constitute the phase shift mask as is generally known, thereflective mask adapted to the extreme ultraviolet radiation has a quitedifficulty in configuring the phase shift mask. For instance, thetransparent mask allows regions different in optical phase difference by180° to be formed using a means of digging in a mask blank, in whichcase, however, an application of the above means to the reflective maskas it is causes also a change of an optical reflectance simultaneouslywith a digging-in of the mask blank, resulting in a failure toconstitute the phase shift mask. Further, the transparent mask alsoallows the regions different in optical phase difference by 180° to beformed by taking advantage of a phase shift effect of a material, inwhich case, however, the application of the above phase shift effect tothe reflective mask provides no constitution having a desiredreflectance and the phase shift effect with a single material, becauseof an absence of a non-absorbent material for an exposure wavelength ofthe extreme ultraviolet radiation, resulting in the failure toconstitute the phase shift mask. Furthermore, a reflective mask blankwith multilayered films used for the reflective mask adapted to theextreme ultraviolet radiation is generally available in the form of astructure (composed of repeated layers as many as 40 layers, forinstance) in which a Si (Silicon) layer and a Mo (Molybdenum) layer arealternately arranged in multiple layers, so that a technology has beenproposed, in which regions whose orders of arrangements of the multiplelayers are reversed to each other are formed individually to provide theregions having the phase difference of 180° and being equal inreflectance. However, it is quite difficult to fabricate a multilayeredstructure as described the above, resulting in no practical use of thephase shift mask of the above multilayered structure yet. For the abovereasons, the reflecting phase shift mask adapted to the extremeultraviolet radiation has been supposed that it is impossible toconstitute this reflecting phase shift mask actually.

Thus, the present invention has been undertaken in view of a fact that arefractive index of a material suitably used as a masking material forthe extreme ultraviolet wavelength is in a range of 0.89 to 1.01, and isthus intended to provide an extreme ultraviolet phase shift mask thatmay be configured actually by obtaining an appropriate combination of arefractive index with an absorption coefficient, a fabrication methodthereof, and a fabrication method of a semiconductor apparatus.

DISCLOSURE OF THE INVENTION

According to the present invention, there is provided an exposure lightphase shift mask devised to attain the above object, that is, anexposure light phase shift mask used to transfer a desired pattern to alight exposed material by a reflection of an exposure light, the phaseshift mask being characterized by having a reflective mask blank withmultilayered films that reflects the exposure light, and a first and asecond regions formed on the reflective mask blank with multilayeredfilms, wherein each film thickness and each complex refractive index ina formative film of the first region and a formative film of the secondregion are set to ensure that a reflected light contained in theexposure light in the first region and a reflected light contained inthe exposure light in the second region form a prescribed phasedifference.

Further, according to the present invention, there is also provided afabrication method of a phase shift mask for an exposure light devisedto attain the above object, that is, a fabrication method of a phaseshift mask for an exposure light having a reflective mask blank withmultilayered films that reflects an exposure light, and a first and asecond regions formed on the reflective mask blank with multilayeredfilms, and is characterized by specifying, with reference to anarbitrary complex refractive index to the exposure light and anarbitrary film thickness of each film formed on the reflective maskblank with multilayered films, a phase and a reflectance of a reflectedlight contained in the exposure light based on the above complexrefractive index and the above film thickness, and by selecting, basedon the specified phase and the specified reflectance, each filmthickness and each complex refractive index in a formative film of thefirst region and a formative film of the second region to ensure thatthe reflected light contained in the exposure light in the first regionand the reflected light contained in the exposure light in the secondregion create a prescribed phase difference.

Furthermore, according to the present invention, there is also provideda fabrication method of a semiconductor apparatus devised to attain theabove object, that is, a fabrication method of a semiconductor apparatusincluding a lithography process of transferring a desired pattern to alight exposed material using an exposure light phase shift mask, and ischaracterized by specifying, with reference to an arbitrary complexrefractive index to the exposure light and an arbitrary film thicknessof each film formed on a reflective mask blank with multilayered films,a phase and a reflectance of a reflected light contained in the exposurelight based on the above complex refractive index and the above filmthickness, by selecting, based on the specified phase and the specifiedreflectance, each film thickness and each complex refractive index in aformative film of the first region and a formative film of the secondregion to ensure that the reflected light contained in the exposurelight in the first region and the reflected light contained in theexposure light in the second region create a prescribed phasedifference, by forming the formative film of the first region and theformative film of the second region on the reflective mask blank withmultilayered films based on the selected complex refractive index andthe selected film thickness to constitute an exposure light phase shiftmask having the first region and the second region on the reflectivemask blank with multilayered films, and by transferring the desiredpattern to the light exposed material using the resultant exposure lightphase shift mask.

According to the phase shift mask for the exposure light having theabove constitution, the fabrication method of the phase shift mask usingthe above procedure and the fabrication method of the semiconductorapparatus using the above procedure, the first and the second regionsformed on the reflective mask blank with multilayered films require thatthe film thickness and the complex refractive index in each of the firstand the second regions are set to ensure that the reflected lightcontained in the exposure light in the first and the second regionscreates the prescribed phase difference. Specifically, the formativefilms of the first and the second regions are deposited to reach the setfilm thickness, and each composing material of the formative films ofthe first and the second regions is selected to reach the set complexrefractive index. The set complex refractive index may be reached byproviding each formative film in the form of a multilayered structureconsisting of a plurality of materials. Each film thickness and eachcomplex refractive index in the formative films of the first and thesecond regions are adjusted to reach the set values as described theabove, resulting in a creation of the prescribed phase difference (180°,for instance) in the reflected light contained in the exposure lightbetween the first region and the second region.

The present invention is characterized in that the exposure light is theextreme ultraviolet radiation, X-rays, radioactive rays, ultravioletrays, or a visible light. Further, it is also characterized in that thephase shift mask is a halftone phase shift mask or a Levenson phaseshift mask.

Furthermore, the present invention is also characterized in that eachfilm thickness and each complex refractive index in the formative filmof the first region and the formative film of the second region are setusing an iso-phase contour line and an iso-reflectance contour line, andthe iso-phase contour line is calculated by fixing an imaginary part ofthe complex refractive index.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are schematic views showing one example of a schematicconfiguration of a phase shift mask according to the present invention.

FIG. 2 is a flowchart showing a fabrication procedure of the phase shiftmask in a first embodiment of the present invention.

FIG. 3 illustrates one specific example of an iso-phase contour line.

FIG. 4 illustrates one specific example of an iso-reflectance contourline.

FIG. 5 illustrates a real part distribution of a composite complexrefractive index to a Ru film thickness and a TaN film thickness toobtain a halftone phase shift mask.

FIG. 6 illustrates a relation between a total film thickness in thehalftone phase shift mask and a real part (n) of the composite complexrefractive index and a reflectance (k).

FIG. 7 illustrates a relation between the total film thickness in thehalftone phase shift mask and the Ru film thickness and the TaN filmthickness.

FIG. 8 illustrates an imaginary part distribution of the compositecomplex refractive index to the Ru film thickness and the TaN filmthickness to obtain the halftone phase shift mask.

FIG. 9 illustrates one example of a matrix-shaped arrangement of a phasedifference and a half tone reflectance to a film thickness of a Ru layerand a film thickness of a TaN layer.

FIG. 10 illustrates one example of the matrix-shaped arrangement of thephase difference to the film thickness of the Ru layer and the filmthickness of a Cr layer.

FIG. 11 illustrates one example of the matrix-shaped arrangement of thehalf tone reflectance to the film thickness of the Ru layer and the filmthickness of the Cr layer.

FIG. 12 illustrates a light intensity distribution as for a hole patternhaving a mask hole opening of 30 nm (indicated with wafer coordinates)in the case where a NA of the halftone phase shift mask is NA=0.25.

FIG. 13 is a schematic view showing a sectional structure of oneconfiguration of the halftone phase shift mask.

FIG. 14 is a flowchart showing a fabrication procedure of the phaseshift mask in a second embodiment of the present invention.

FIG. 15 illustrates one specific example of the iso-phase contour line.

FIG. 16 is a schematic view showing a sectional structure of oneconfiguration (a structure 1) of a Levenson phase shift mask.

FIG. 17 illustrates one example of an optimization (with a Mo filmthickness as a parameter) of a phase and a reflectance withconsiderations of a multiple interference in film in the Levenson phaseshift mask of the structure 1.

FIG. 18 illustrates the light intensity distribution in the Levensonphase shift mask of the structure 1.

FIG. 19 illustrates the phase difference (indicated on the wafer) of theLevenson phase shift mask of the structure 1.

FIG. 20 illustrates one example of a deposition procedure (Part 1) ofthe Levenson phase shift mask of the structure 1.

FIG. 21 illustrates one example of the deposition procedure (Part 2) ofthe Levenson phase shift mask of the structure 1.

FIG. 22 illustrates one example of the deposition procedure (Part 3) ofthe Levenson phase shift mask of the structure 1.

FIG. 23 illustrates one example of the deposition procedure (Part 4) ofthe Levenson phase shift mask of the structure 1.

FIG. 24 is a schematic view showing a sectional structure of a differentconstitution (a structure 2) of the Levenson phase shift mask.

FIG. 25 illustrates one example of the optimization (with the Mo filmthickness as the parameter) of the phase and the reflectance withconsiderations of the multiple interference in film in the Levensonphase shift mask of the structure 2.

FIG. 26 illustrates the light intensity distribution in the Levensonphase shift mask of the structure 2.

FIG. 27 illustrates the phase difference (indicated on the wafer) of theLevenson phase shift mask of the structure 2.

FIG. 28 is a schematic view showing a sectional structure of a furtherdifferent constitution (a structure 3) of the Levenson phase shift mask.

FIG. 29 illustrates one example of the optimization (with the Mo filmthickness as the parameter) of the phase and the reflectance withconsiderations of the multiple interference in film in the Levensonphase shift mask of the structure 3.

FIG. 30 illustrates the light intensity distribution in the Levensonphase shift mask of the structure 3.

FIG. 31 illustrates the phase difference (indicated on the wafer) of theLevenson phase shift mask of the structure 3.

FIG. 32 is a schematic view showing a sectional structure of oneconstitution (a structure 4) in which a first region and a second regionof the Levenson phase shift mask are in a flat form.

FIG. 33 illustrates one example of the optimization (with the Mo filmthickness as the parameter) of the phase and the reflectance withconsiderations of the multiple interference in film in the Levensonphase shift mask of the structure 4.

FIG. 34 illustrates the light intensity distribution in the Levensonphase shift mask of the structure 4.

FIG. 35 illustrates the phase difference (indicated on the wafer) in theLevenson phase shift mask of the structure 4.

FIG. 36 illustrates one example of the deposition procedure (Part 3) ofthe Levenson phase shift mask of the structure 4.

FIG. 37 illustrates one example of the deposition procedure (Part 4) ofthe Levenson phase shift mask of the structure 4.

FIG. 38 is a schematic view showing a sectional structure of a differentflat constitution (a structure 5) of the Levenson phase shift mask.

FIG. 9 illustrates one example of the optimization (with the Mo filmthickness as the parameter) of the phase and the reflectance withconsiderations of the multiple interference in film in the Levensonphase shift mask of the structure 5.

FIG. 40 illustrates the light intensity distribution in the Levensonphase shift mask of the structure 5.

FIG. 41 illustrates the phase difference (indicated on the wafer) of theLevenson phase shift mask of the structure 5.

FIG. 42 is a schematic view showing a sectional structure of a furtherdifferent flat constitution (a structure 6) of the Levenson phase shiftmask.

FIG. 43 illustrates one example of the optimization (with the Mo filmthickness as the parameter) of the phase and the reflectance withconsiderations of the multiple interference in film in the Levensonphase shift mask of the structure 6.

FIG. 44 illustrates the light intensity distribution in the Levensonphase shift mask of the structure 6.

FIG. 45 illustrates the phase difference (indicated on the wafer) in theLevenson phase shift mask of the structure 6.

FIG. 46 illustrates the light intensity distribution (NA=0.25) to a maskTaN width (indicated on the wafer) in the Levenson phase shift mask ofthe structure 5.

FIG. 47 illustrates the light intensity distribution (NA=0.25) to themask TaN width (indicated on the wafer) in a conventional binary mask.

FIG. 48 illustrates the light intensity distribution (NA=0.30) to themask TaN width (indicated on the wafer) in the Levenson phase shift maskof the structure 5.

BEST MODE FOR CARRYING OUT THE INVENTION

A phase shift mask for an exposure light, a method thereof, and afabrication method of a semiconductor apparatus according to the presentinvention are hereinafter described with reference to the accompanyingdrawings by taking a case where an exposure light is specified as anextreme ultraviolet radiation. Incidentally, it is a matter of coursethat the present invention is not limited to embodiments describedbelow.

(Description of Schematic Constitution of Phase Shift Mask)

Firstly, a schematic constitution of a phase shift mask for an extremeultraviolet radiation according to the present invention is described.The phase shift mask described here in is used to transfer a desiredpattern (a circuit pattern, for instance) to a light exposed materialsuch as a wafer by a reflection of the extreme ultraviolet radiation ina lithography process included in the fabrication method ofsemiconductor apparatus. Incidentally, an ultraviolet light having ashorter wavelength (in the range of 1 nm or above to 100 nm or below,for instance) than that of an ultraviolet light having been employed ina conventional lithography process, specifically, an ultraviolet lighthaving a wavelength of 13.5 nm, for instance, is applicable to “theextreme ultraviolet radiation” specified herein.

FIGS. 1A and 1B are schematic views showing one example of the schematicconstitution of the phase shift mask according to the present invention.As shown in these figures, each of phase shift masks 10, 10′ includes areflective mask blank with multilayered films (mask blanks) 11 thatreflects the extreme ultraviolet radiation, and a first and a secondregions 12 a and 12 b that are formed on the reflective mask blank withmultilayered films 11.

The reflective mask blank with multilayered films 11 is in the form of astructure in which a Si (Silicon) layer and a Mo (Molybdenum) layer arealternately arranged in multiple layers, in which case, a structurecomposed of repeated multiple layers as many as 40 layers is generallyemployed. Further, it is known that in terms of a ratio Γ of a totalthickness of the Si layer and the Mo layer to a thickness of the Molayer, a Mo layer thickness/(Si layer thickness+Mo layer thickness)ratio=0.4 is adequate. Thus, assuming that a wavelength λ of the extremeultraviolet radiation for use in an exposure is 13.5 nm, the reflectivemask blank with multilayered films 11 requires that the total filmthickness of the Si layer and the Mo layer reaches(λ/2)/(0.9993×0.6+0.9211×0.4)=6.973 nm, where the Si layer is supposedto have a thickness of 6.9730×0.6=4.184 nm, and the Mo layer is supposedto have a thickness of 6.9730×0.4=2.789 nm.

The reflective mask blank with multilayered films 11 has thereon anabsorption film 14 through a buffer film 13. The buffer film 13 isprovided as an etching stopper being operative when forming theabsorption film or for the purpose of avoiding damages at the time of aremoval of defects after a formation of the absorption film, and isformed with a Ru (Ruthenium) layer or SiO₂ (Silicon Dioxide), forinstance. The absorption film 14 consists of an extreme ultravioletabsorbing material, and is formed with a TaN (Tantalum Nitride) layer,for instance. However, the absorption film 14 may be one consisting of adifferent material as long as it is available as an extreme ultravioletmasking material. Specifically, Ta (Tantalum) or Ta compounds, Cr(Chromium) or Cr compounds and W (Tungsten) or W compounds, etc. aresupposed to be available, in addition to the TaN.

By the way, the reflective mask blank with multilayered films 11 hasthereon the first region 12 a and the second region 12 b. The firstregion 12 a and the second region 12 b are supposed to create aprescribed phase difference (180°, for instance) in the reflected lightcontained in the extreme ultraviolet radiation in each of the aboveregions.

Thus, the first region 12 a and the second region 12 b differ in acomposing material or a thickness of a formative film (the buffer film13+the absorption film 14) in each of the above regions (See FIG. 1A),as described later. However, it is also allowable to form the bufferfilm 13 and the absorption film 14 only on either of the above regionsto ensure that the first region 12 a and the second region 12 b createthe phase difference (See FIG. 1B).

Assuming that a phase difference between an incident light and areflected light in the first region 12 a is φ₁, a phase differencebetween an incident light and a reflected light in the second region 12b is φ_(2.) and a difference in the film thickness between the firstregion 12 a and the second region 12 b is h, a phase difference φbetween the first region 12 a and the second region 12 b maybe specifiedwith the following expression (1).ψ(λ)=φ₁(λ)−φ₂(λ)+(4πh cosθ)/λ  (1)

In the expression (1), the θ is an angle that the light incident on themask forms with respect to a normal on a mask surface. A reference λ isan exposure center wavelength. References φ₁ and φ₂ may be thoseobtained using a method disclosed by “Yamamoto and T. Namioka”“Layer-by-layer design method for soft-x-ray multilayers”, AppliedOptics, Vol. 31 pp 1622 to 1630, (1992), for instance.

Further, a complex refractive index of the composing material of each ofthe first region 12 a and the second region 12 b is required tocalculate the phase difference φ(λ) using the expression (1). In thecase where the extreme ultraviolet radiation has the exposure centerwavelength of 13.5 nm, the complex refractive index of each composingmaterial results in Mo: 0.92108−0.00643543i, Si: 0.9993−0.00182645i, Ru:0.88749−0.0174721i and TaN: 0.94136−0.0315738i, for instance. When thecomposing materials are in the form of a multilayered structure composedof arbitrary m layers, a composite complex refractive index obtainedwith the following expressions (2) and (3) may be used. $\begin{matrix}{n = {\sum\limits_{1}^{m}{n_{m}{d_{m}/{\sum\limits_{1}^{m}d_{m}}}}}} & (2) \\{k = {\sum\limits_{1}^{m}{k_{m}{d_{m}/{\sum\limits_{1}^{m}d_{m}}}}}} & (3)\end{matrix}$

The phase shift masks 10, 10′ require that the composing material (thecomplex refractive index, in particular) and the thickness of theformative film (the buffer film 13+the absorption film 14) in each ofthe first and the second regions 12 a and 12 b are set to ensure thatthe first and the second regions 12 a and 12 b allow the phasedifference φ specified as described the above to reach the prescribedvalue (180°, for instance). That is, the phase shift masks 10, 10′described in the embodiment of the present invention have great featuresin that each film thickness and each complex refractive index in theformative film of the first region 12 a and the formative film of thesecond region 12 b are set to ensure that the reflected light containedin the extreme ultraviolet radiation in the first region 12 a and thereflected light contained in the extreme ultraviolet radiation in thesecond region 12 b create the prescribed phase difference.

Description of Fabrication Procedure of Phase Shift Mask

A fabrication procedure of the phase shift masks 10, 10′ having theabove features is now described. However, a description in this sectionis given by classifying the above fabrication procedure into a firstembodiment and a second embodiment.

First Embodiment

The first embodiment is described by taking the case where the presentinvention is applied to constitute a halftone phase shift mask. FIG. 2is a flow chart showing the fabrication procedure of the phase shiftmask in the first embodiment.

In a fabrication of the halftone phase shift mask, an iso-phase contourline and an iso-reflectance contour line to each complex refractiveindex are firstly calculated (Step 101, where Step is hereinafterabbreviated to “S”). A calculation of the iso-phase contour line and theiso-reflectance contour line is required for an arbitrary complexrefractive index without being limited to the existing material. Thatis, with reference to the arbitrary complex refractive index to theextreme ultraviolet radiation, a phase and a reflectance of thereflected light contained in the extreme ultraviolet radiation based onthe above arbitrary complex refractive index are specified.Incidentally, the phase and the reflectance to the complex refractiveindex may be specified theoretically uniquely. Further, it is alsosupposed that the arbitrary complex refractive index includes a complexrefractive index of the reflective mask blank with multilayered films11. That is, the calculation of the iso-phase contour line and theiso-reflectance contour line is also required for the reflective maskblank with multilayered films 11.

FIG. 3 illustrates one specific example of the iso-phase contour line.The illustrated iso-phase contour line is calculated by fixing animaginary part (k) of the complex refractive index at 0.0100i. Further,FIG. 4 illustrates one specific example of the iso-reflectance contourline. The illustrated iso-reflectance contour line is calculated byfixing a real part (n) of the complex refractive index at 0.9100.Incidentally, in the illustrated iso-phase contour line andiso-reflectance contour line, an exposure wavelength denoted by λ in theexpression (1) is 13.5 nm, and an incident angle of the light obliquelyincident on the mask as denoted by θ is 4.84°.

The reflectance and the phase respectively depend on the real part andthe imaginary part of the complex refractive index, in which case, thephase is supposed to be mainly dependent on the real part of the complexrefractive index, while the reflectance is supposed to be mainlydependent on the imaginary part of the complex refractive index. Thus,the first region 12 a and the second region 12 b may finally obtain thephase difference of 180° and the desired reflectance only by setting thecomplex refractive index or the film thickness of the composing materialof each of the regions 12 a and 12 b using the iso-phase contour line inFIG. 3 and the iso-reflectance contour line in FIG. 4 in an approximatecalculation manner. Alternatively, it is also allowable to set both thecomplex refractive index and the film thickness.

In setting the complex refractive index or the film thickness, amaterial workable into the first and the second regions 12 a and 12 b onthe reflective mask blank with multilayered films 11 and a filmcomposition are firstly obtained (S102). Then, the complex refractiveindex in a material composition of the first region 12 a and the complexrefractive index in the material composition of the second region 12 bare respectively calculated (S103, S104).

It is assumed that the case of a fabrication of the halftone phase shiftmask 10′ having the constitution shown in FIG. 1B, for instance, thatis, a phase shift mask having the absorption film 14 only on the secondregion 12 b through the buffer film 13 to ensure that the first region12 and the second region 12 b create the phase difference of 180°. Inthis case, each of the first region 12 a and the second region 12 b issupposed to obtain a desired reflectance (a mutually different value),respectively. Further, as for the second region 12 b, Ru and TaN aresupposed to be selected respectively as the composing material of thebuffer film 13 and the composing material of the absorption film 14.

FIG. 5 illustrates a real part distribution of the complex refractiveindex to a Ru film thickness and a TaN film thickness. It maybeappreciated from this illustration that the real part of the compositecomplex refractive index is capable of taking values ranging from 0.890to 0.945 when the Ru film thickness varies from 1 nm to 20 nm and theTaN film thickness varies from 1 nm to 50 nm. That is, the complexrefractive index in the material composition of the second region 12 bmay be found from the contents of FIG. 5. Incidentally, the first region12 a does not have either of the buffer film 13 and the absorption film14, so that the complex refractive index may be calculated from themultilayered structure of the reflective mask blank with multilayeredfilms 11.

After the calculation of the respective complex indexes of refraction, adifference in a level of the formative film between the first region 12a and the second regions 12 b, that is, the thickness of the formativefilm of the second region 12 b is calculated from a refractive index inthe first region 12 a, a refractive index in the second region 12 b andthe already calculated iso-phase contour line (S105). Specifically, ifthe calculation is performed based on the distribution of the complexindexes of refraction in FIG. 5 and the iso-phase contour line diagramin FIG. 3, a relation between the real part (n) of the composite complexrefractive index and the total film thickness of the formative film (thebuffer film 13+the absorption film 14) required for the phase differencefrom the reflective mask blank with multilayered films 11 to reach 180°is calculated uniquely as shown in FIG. 6. Further, the film thicknessof each of the Ru layer (the buffer film 13) and the TaN layer (theabsorption film 14) required for the phase difference from thereflective mask blank with multilayered films 11 to reach 180° iscalculated uniquely as shown in FIG. 7 based on a condition under whichthe composite complex refractive index provides the phase difference of180°. The calculation of the thickness of the formative film of thesecond region 12 b, that is, the film thickness of each of the Ru layerand the TaN layer will do in this manner.

After the film thickness of each of the Ru layer and the TaN layer isobtained, the extreme ultraviolet reflectance in the formative film ofthe first region 12 a and in the second region 12 b is then calculated(S106). The reflectance may be obtained by calculating the imaginarypart (k) of the composite complex refractive index to the total filmthickness from the film thickness of each of the Ru layer and the TaNlayer to calculate the reflectance from the calculated imaginary part ofthe composite complex refractive index. FIG. 8 illustrates a relationbetween the film thickness of each of the Ru layer and the TaN layer andthe imaginary part (k) of the composite complex refractive index to thetotal film thickness. Further, if the imaginary part (k) of the complexrefractive index is known, the reflectance is obtained uniquely from theiso-reflectance contour line shown in FIG. 4. In FIG. 6, there is alsoshown a relation between the imaginary part (k) of the composite complexrefractive index and the reflectance and the total film thickness.

When the reflectance is set at 0.075, for instance, the total filmthickness of 43 nm is derived from the contents of FIG. 6, in whichcase, 14 nm in the film thickness of the Ru layer and 29 nm in the filmthickness of the TaN layer are obtained as the most adaptable conditionsfrom the contents of FIG. 7. A halftone phase shift having a phasedifference of 182.4° and a reflectance of 0.075 is supposed to beobtained by calculating, with reference to this film thickness, thephase difference and the reflectance further using an accurate value ofthe composite complex refractive index as described later.

However, according to the contents of FIG. 6, it may be seen that a filmthickness condition required for the reflectance to be set at 0.075 isexistent also in the vicinity of 46.3 nm and 48.3 nm in the total filmthickness. That is, the total film thickness is not one determined as asingle condition from the complex refractive index, and therefore, needsto be determined in consideration of various conditions syntheticallyinclusive of a film thickness adjustment described below. In this case,it is desirable to set at a flat change portion of the total filmthickness in FIG. 6 (in the vicinity of 50.5 nm, for instance) tolargely make sure of a process margin for the complex refractive indexto film thickness variations in a mask fabrication. Thus, even if thetotal film thickness varies in the range of about ±1.5 nm, the complexrefractive index is unchanged, so that the phase difference and thereflectance also remain unchanged.

Thereafter, the film thickness adjustment is further performed so thatthe first region 12 a and the second region 12 b obtain the phase of180° and the desired reflectance (S107, S108). A further given reasonfor the film thickness adjustment is to obtain the desired phase and thedesired reflectance inclusive of a multiple interference effect in filmthat is not taken into consideration in FIG. 6. Specifically, each phasedifference and each half tone reflectance applicable to the case ofappropriate variations of the film thickness of the Ru layer and thefilm thickness of the TaN layer are calculated according to a proceduredescribed the above. FIG. 9 illustrates one example of a matrix-shapedarrangement of the phase difference and the half tone reflectance to thefilm thickness of the Ru layer and the film thickness of the TaN layer.The half tone reflectance is herein specified as a difference betweenthe reflectance of the first region 12 a and the reflectance of thesecond region 12 b in the phase shift mask 10′ shown in FIG. 1B. Then, awindow satisfying the desired phase difference and the desired half tonereflectance, that is, a set value of the film thickness obtained afterthe adjustment may be selected from these results. Incidentally, in FIG.9, there is shown the case of the phase difference of 180.0±6° and thehalf tone reflectance of 9.0±1%, and the case of the phase difference of180.0±6° and the half tone reflectance of 5.0±1% (See a shadow part inFIG. 9). Thus, the halftone phase shift having the phase difference of179.4° and the half tone reflectance of 9.5% is supposed to be obtainedby setting the film thickness of the Ru layer at 13 nm and the filmthickness of the TaN layer at 30 nm. Herein, the reflectance reaches0.0070, which approximately agrees with an estimated value obtained inFIG. 6. FIGS. 10 and 11 illustrate different matrix-shaped arrangementsof the phase difference and the half tone reflectance to the filmthickness of the Ru layer and the film thickness of a Cr layer. Thus,the half tone phase shift mask having the phase difference of 179.2° andthe halftone reflectance of 4.1% is supposed to be obtained by settingthe film thickness of the Ru layer at 9 nm and the film thickness of theCr layer at 34 nm.

The setting of the complex refractive index and the thickness of theformative film of the second region 12 b as described the above may befollowed by a deposition of the above formative film on the reflectivemask blank with multilayered films 11 according to the above setting toconstitute the halftone phase shift mask. Incidentally, the depositionof the formative film may be performed using a well-known technology,and therefore, a description thereof is herein omitted.

That is, the phase difference from the reflective mask blank withmultilayered films 11 in the second region 12 b is calculated from thefilm thickness and the real part of the complex refractive index of agroup of the materials composing the second region 12 b formed on thereflective mask blank with multilayered films 11, and the reflectance inthe second region 12 b is calculated from the film thickness and theimaginary part of the complex refractive index of the group of thematerials composing the second region 12 b, thereby providing, based onthe calculated phase difference and the calculated reflectance, thehalftone phase shift mask of the above constitution, that is, one inwhich the first region 12 a (the reflective mask blank with multilayeredfilms 11) and the second region 12 b are different in the phasedifference by 180° and the reflectance of the second region 12 b reachesa desired value. However, it does not matter if the calculation on whichof the phase difference and the reflectance is performed earlier.

A light intensity distribution in the case of the use of the halftonephase shift mask obtained according to the above procedure is described.FIG. 12 illustrates the light intensity distribution as for a holepattern having a mask hole opening of 30 nm (indicated with wafercoordinates, where a four-fold mask requires the hole opening of 120nm), when optical conditions of NA=0.25 and σ=0.70 are applied. In FIG.12, there is also shown the light intensity distribution as for aconventional binary mask, for a comparison. According to thisillustration, it is apparent that the use of the halftone phase shiftmask enables an effect of increasing a pattern edge contrast to beobtained, as compared with the conventional binary mask.

Incidentally, while the phase shift mask 10′ of the constitution shownin FIG. 1B, that is, one having the buffer film 13 and the absorptionfilm 14 only on the second region 12 b is taken as the instance of thehalftone phase shift mask, it is also allowable to constitute thehalftone phase shift mask 10 as shown in FIG. 1A, for instance. However,even in the case of the halftone phase shift mask 10, the first region12 a and the second region 12 b require that the film thickness and thecomplex refractive index of the formative film of each of the aboveregions are set to ensure that the phase difference of 180° is created,as described the above.

FIG. 13 is a schematic view showing a sectional structure of oneconstitution of the halftone phase shift mask. In the illustrated mask,the reflective mask blank with multilayered films 11 has thereon thefirst region 12 a in which Ru of 10 nm and Si of 47 nm are multilayeredin order, and the second region 12 b in which Ru of 5 nm, TaN of 47 nmand Ru of 5 nm are multilayered in order. The reason for the use of theSi for the composing material of the formative film of the first region12 a is as follows. The complex refractive index of the Si is0.99932−0.00182645i whose real part is extremely close to 1 specified asthe refractive index in a vacuum and whose imaginary part is smallerthan that of the other materials. Thus, a Si material is allowed to beara role in the adjustment of the phase difference and the reflectanceratio by taking advantage of the multiple interference effect in film ofthe Si material. The application of the multiple interference effect infilm makes it possible to constitute the halftone phase shift mask of aflat structure in which the first region 12 and the second region 12 bcreate the phase difference of 180°, and besides, respectively have acompletely flat upper surface.

Second Embodiment

The second embodiment of the fabrication procedure of the phase shiftmask is now described. A description of the second embodiment is givenby taking the case where the present invention is applied to constitutea Levenson phase shift mask. FIG. 14 is a flowchart showing thefabrication procedure of the phase shift mask in the second embodiment.

As shown in FIG. 14, the fabrication of the Levenson phase shift mask isalso performed approximately in the same manner (See FIG. 2) as that inthe case of the halftone phase shift mask in the above first embodiment(S201 to S208). However, the Levenson phase shift mask is different fromthe halftone phase shift mask in that the former requires that not onlythe phases in the first region 12 a and the second region 12 b aredifferent by 180°, but also the reflectance in the first region 12 a andthat in the second region 12 b are approximately equal. That is, forconstituting the Levenson phase shift mask, it is necessary to satisfytwo requirements, that is, (1) the reflectance in the first region 12 aand that in the second region 12 b should be approximately equal, and(2) the phase difference between the first region 12 a and the secondregion 12 b should be 180° (S208).

A judgment as to whether or not these requirements are satisfied maybeperformed as follows. Firstly, assuming that the reflectance of thefirst region 12 a is R₁, and the reflectance of the second region 12 bis R₂, a reflectance ratio P obtained by the following expression (4) isspecified.P=(1−R ₁(λ)/R ₂(λ))×100(%)   (4)

Then, a criterion 1 of |P|≦3.0% is applied to the specified reflectanceratio P, and when an agreement with the criterion 1 is reached, it isjudged that the above requirement (1) is satisfied.

Further, with reference to the above requirement (2), a criterion 2 of|φ(λ)|≦6° is applied to φ(λ) obtained by the expression (1) having beendescribed in the first embodiment. Then, when an agreement with thecriterion 2 is reached, it is judged that the above requirement (2) issatisfied.

The Levenson phase shift mask obtained in this manner is supposed to beavailable in the form of the constitution shown in FIG. 1A, that is, onein which both the first region 12 a and the second region 12 b have thebuffer film 13 and the absorption film 14.

A fabrication procedure of the Levenson phase shift mask of theconstitution shown in FIG. 1A is now described in more detail by takinga specific example. For constituting the Levenson phase shift mask, thecalculation of the iso-phase contour line and the iso-reflectancecontour line to the arbitrary complex refractive index is also firstlyrequired, like the case of the halftone phase shift mask having beendescribed in the first embodiment. FIG. 15 illustrates one specificinstance of the iso-phase contour line. The illustrated iso-phasecontour line is calculated by fixing the imaginary part (k) of thecomplex refractive index at 0.01000i.

By the way, the Levenson phase shift mask requires that a phasedifference φ₁(λ) between the formative film of the first region 12 a andthe reflective mask blank with multilayered films 11 is specified by thefollowing expression (5).ψ₁(λ)=φ₁(λ)−φs(λ)+(4πh ₁ cosθ)/λ  (5)

Further, a phase difference φ₂ between the formative film of the secondregion 12 b and the reflective mask blank with multilayered films 11 isspecified by the following expression (6).ψ₂(λ)=φ₂(λ)−φs(λ)+(4πh ₂ cos θ)/λ  (6)

Thus, a phase difference φ(λ) between the first region 12 a and thesecond region 12 b is supposed to be specified by the followingexpression (7).ψ(λ)=ψ₁(λ)−ψ₂(λ)   (7)

A relation specified by the expression (7) is expressed in terms of acorrelation of the iso-phase contour lines as shown in FIG. 15. In FIG.15, it may be appreciated that the difference in the level between thefirst region 12 a and the second region 12 b requires 56 nm to satisfythe phase difference of 180° between the first region 12 a and thesecond region 12 b with the material whose real part of the complexrefractive index is 0.94, for instance (See “1” in FIG. 15). Further, itmay be also appreciated that the difference in the level between thefirst region 12 a and the second region 12 b requires 42 nm to satisfythe phase difference of 180° between the first region 12 a and thesecond region 12 b with the material whose real part of the complexrefractive index is 0.96 in the first region 12 a and 0.94 in the secondregion 12 b (See “2” in FIG. 15). On the contrary, for the calculationof the reflectance, an absolute value to the total film thickness isused as it is, instead of a relative value.

The Levenson phase shift mask may be also constituted only by setting,based on the iso-phase contour line (See FIG. 15) and theiso-reflectance contour line (See FIG. 4) as described the above, thefilm thickness and the complex refractive index of the formative film soas to satisfy the criteria 1 and 2.

That is, the phase difference from the reflective mask blank withmultilayered films 11 in the first region 12 a is calculated from thefilm thickness and the real part of the complex refractive index of thegroup of the materials composing the first region 12 a formed on thereflective mask blank with multilayered films 11, and the phasedifference from the reflective mask blank with multilayered films in thesecond region 12 b is calculated from the film thickness and the realpart of the complex refractive index of the group of the materialscomposing the second region 12 b formed on the reflective mask blankwith multilayered films 11. Further, the reflectance in the first region12 a is calculated from the film thickness and the imaginary part of thecomplex refractive index of the group of the materials composing thefirst region 12 a formed on the reflective mask blank with multilayeredfilms 11, and the reflectance in the second region 12 b is furthercalculated from the film thickness and the imaginary part of the complexrefractive index of the group of the materials composing the secondregion 12 b formed on the reflective mask blank with multilayered films11. Then, these results are applied to obtain, as the Levenson phaseshift mask, the constitution satisfying the criteria 1 and 2, that is,one in which the first region 12 a and the second region 12 b aredifferent in the phase difference by 180°, and the reflectance in thefirst region 12 a and that in the second region 12 b are approximatelyequal. Incidentally, it does not matter if the calculation on which ofthe phase difference and the reflectance is performed earlier.

By the way, it is necessary to deposit the formative films of the firstregion 12 a and the second region 12 b with different materials arrangedappropriately in multiple layers to satisfy the criteria 1 and 2simultaneously. This is because the Levenson phase shift masksimultaneously satisfying the criteria 1 and 2 fails to be obtained as apractically easily fabricated structure due to limitations on thecomplex refractive index of the practically existing materials, unlessthe different materials are appropriately arranged in multiple layers.

For this reason, TaN, Ru and Si are used as the materials composing thefirst region 12 a. Further, Mo and Ru are used as the materialscomposing the second region 12 b. The reason for the use of thesematerials is that it is generally known that an etching selection ratioof each material is quite largely taken in a combination as describedbelow, as disclosed in “Approach to patterning of extreme ultravioletlithography masks” of Jpn. J. Appl. Phys, Vol. 40 (2001), pp. 6998 to7001. That is, when an etching of the Ru layer to a Si substrate isperformed by a dry etching with Cl₂+O₂ gas, the Si substrate acts as anetching stopper on the Ru etching. When the etching of the TaN layer tothe Ru substrate is performed by the dry etching with Ar+Cl₂ gas, the Rusubstrate acts as the etching stopper on the TaN layer etching. Further,the etching of the Mo layer and the Si layer to the Ru substrate is alsoperformed by the dry etching with the Ar+Cl₂ gas to largely take theselection ratio. This is because a Ru chloride RuCl₃ is a relativelystable substance which is supposed to be dissolved at 600° C. or above.On the contrary, a Si chloride SiCl₄ has a boiling point of 57.6° C., aMo chloride MoCl₅ has a boiling point of 268° C., and a Ta chlorideTaCl₅ has a boiling point of 242° C., from which it may be seen that aremoval as etching reaction gas in the vacuum to the Ru chloride iseasily caused.

FIG. 16 is a schematic view showing a sectional structure of oneconstitution of the Levenson phase shift mask. The illustrated structure(which is hereinafter referred to as “a structure 1”) is supposed to beone satisfying the criteria 1 and 2 determined based on the iso-phasecontour line in FIG. 15 and the iso-reflectance contour line in FIG. 4.The first region 12 a has, on the reflective mask blank withmultilayered films 11, the formative film in the form of the multiplelayers in the order of Ru of 2 nm, TaN of 7 nm and Ru of 4 nm. The firstregion 12 a has the total film thickness of 11 nm, and shows thecomposite complex refractive index whose real part is 0.9165, and whoseimaginary part is 0.02507i. Further, the second region 12 b has theformative film in the form of the multiple layers in the order of Ru of4 nm, Mo of 49 nm and Ru of 2 nm. The second region 12 b has the totalfilm thickness of 55 nm, and shows the composite complex refractiveindex whose real part is 0.9174 and whose imaginary part is 0.00764i.Incidentally, a boundary between the first region 12 a and the secondregion 12 b has a TaN absorption layer of 120 nm in the film thicknesswith a width of 40 nm.

With reference to the above structure 1, the calculation of thedifference in the level between the first region 12 a and the secondregion 12 b from the iso-phase contour line in FIG. 15 results in 43 nmof the above difference in the level based on a relation between theiso-phase contour lines of 90° and 270°, and similarly, 43 nm is alsoderived from the relation between the iso-phase contour lines of 180°and 0°. Further, according to an iso-transmittance contour line in FIG.4, it may be also appreciated that the reflectance of the first region12 a is 0.39, and the reflectance of the second region 12 b is 0.38.Then, a result as shown in FIG. 17, for instance, is obtained from thecalculation of the phase difference and the reflectance ratio on thestructure 1 by varying the Mo film thickness of the second region 12 binclusive of the multiple interference effect in film in detail. Fromthe illustrated result, it may be confirmed that the structure 1 shownin FIG. 16 is in the form of an optimum constitution within a filmthickness adjustment range of each material.

Further, in the structure 1, the reflectance is 0.0388 with respect tothe first region 12 a, and 0.387 with respect to the second region 12 b,in which case, the reflectance ratio therebetween results in 0.258%.Further, the phase difference between the first region 12 a and thesecond region 12 b reaches 178.8° with respect to a TE (TransverseElectric) wave, and 178.7° with respect to a TM (Transverse Magnetic)wave.

The light intensity distribution in the case of the use of the Levensonphase shift mask of the above structure 1 is supposed to produce aresult as shown in FIG. 18, for instance, when the optical conditions ofNA=0.25 and σ=0.70 are applied to the case of the exposure of the waferto the light with the 120 nm-thick TaN absorption layer formed as wideas 40 nm (10 nm in terms of a wafer unit) on the four-fold mask of thestructure 1.

Further, 180° of the phase difference between the first region 12 a andthe second region 12 b may be confirmed by the calculation of the phasedifference according to the following expression (8) using a 320nm-pitch (a 80 nm-pitch to the width of 10 nm in terms of the waferunit) pattern with the TaN absorption layer having the width of 40 nm.Incidentally, the expression (8) employs coordinates on the wafer. AnX-axis is expressed in terms of nm unit.φ=I(x+80)−1(x) (0≦x≦80)   (8)

FIG. 19 shows a result of the calculation of the expression (8) on aposition right above the mask to a TEy wave, a TMx wave and a TMz wave.According to this illustration, both the TEy wave and the TMx wavesatisfactorily hold the phase difference of 180°. On the contrary, theTMz wave shows a more outstanding deviation from 180°, in which case,however, a contribution toward a transfer is as small as about 0.45%,resulting in no effect on the transfer.

For the above reasons, it may be said that the Levenson phase shift maskof the structure 1 satisfies the criteria 1 and 2 simultaneously toensure that the reflectance in the first region 12 a and that in thesecond region 12 b are approximately equal and the phase differencebetween the first and the second regions is 180°.

A procedure required when depositing, on the reflective mask blank withmultilayered films 11, the formative films of the first and the secondregions 12 a and 12 b respectively obtained after the setting of thecomplex refractive index and the film thickness as described the aboveis now described in brief. FIGS. 20 to 23 illustrate one instance of adeposition procedure of the structure 1. For the deposition of theformative films according to the structure 1, the Ru layer is firstlydeposited on the reflective mask blank with multilayered films 11 by asputtering, as shown in FIG. 20 (a process 1). The Ru layer is supposedto be a material ordinarily available as the buffer layer in the binarymask, so that the same fabrication apparatus as that required for theordinary case maybe used. Then, the TaN layer is deposited on the Rulayer by the sputtering (a process 2). The TaN layer is supposed to bethe material available as the absorption layer in the binary mask, sothat the same fabrication apparatus as that required for the ordinarycase may be used.

Thereafter, the TaN layer is coated with a resist (a process 3), and aremoval of the resist from a second region 12 b portion is performed byway of a patterning and a resist development (a process 4). After theremoval of the resist, the TaN layer is removed from the second region12 b portion by the dry etching with the Ar+Cl₂ gas (a process 5). TheRu layer beneath the etched TaN layer is supposed to function as anetching stopper layer. Then, the resist is separated (a process 6), andthe deposition of the Ru layer again by the sputtering (a process 7) isperformed and is followed by the deposition of the Mo layer this time bythe sputtering (a process 8). The Mo layer is supposed to be thecomposing material of the reflective mask blank with multilayered films11, so that a multilayer fabrication apparatus may be used.

The deposition of the Mo layer is followed by the coating of the resist(a process 9) as shown in FIG. 21, and the removal of the resist from afirst region 12 a portion is performed by way of the patterning and theresist development (a process 10). Then, the Mo layer is removed fromthe first region 12 a portion by the dry etching with the Ar+Cl₂ gas (aprocess 11). The Ru layer beneath the etched Mo layer is supposed tofunction as the etching stopper layer. Thereafter, the resist isseparated (a process 12), and the Ru layer is deposited again by thesputtering (a process 13).

The deposition of the Ru layer is followed by the deposition of the TaNabsorption layer by the sputtering as shown in FIG. 22 (a process 14),and the coating of the resist further follows (a process 15). Then, theremoval of the resist from a portion other than a portion left as theabsorption layer is performed by way of the patterning and the resistdevelopment (a process 16).

Thereafter, the TaN absorption layer is removed by the dry etching withthe Al+Cl₂ gas as shown in FIG. 23 (a process 17). The Ru layer beneaththe etched TaN layer is supposed to function as the etching stopperlayer. Then, a separation of the resist (a process 18) is performed,leading to a completion of the Levenson phase shift mask of thestructure 1 with the effective use of the Ru layer as the etchingstopper layer.

FIG. 24 is a schematic view showing a sectional structure of a differentconstitution of the Levenson phase shift mask. The illustrated structure(which will be hereinafter referred to as “a structure 2”) is supposedto be one satisfying the criteria 1 and 2 determined based on theiso-phase contour line in FIG. 15 and the iso-reflectance contour linein FIG. 4, likewise the above structure 1. The first region 12 a has, onthe reflective mask blank with multilayered films 11, the formative filmin the form of the multiple layers in the order of Ru of 3 nm, TaN of 5nm and Ru of 7 nm. The first region 12 a has the total film thickness of15 nm, and shows the composite complex refractive index whose real partis 0.9054 and whose imaginary part is 0.02217i. Further, the secondregion 12 b has the formative film in the form of the multiple layers inthe order of Ru of 3 nm, Mo of 49 nm and Ru of 4 nm. The second region12 b has the total film thickness of 56 nm, and shows the compositecomplex refractive index whose real part is 0.9169 and whose imaginarypart is 0.00782i.

With reference to the structure 2 as described the above, thecalculation of the difference in the level between the first region 12 aand the second region 12 b from the iso-phase contour line in FIG. 15results in 44 nm of the above difference in the level based on therelation between the iso-phase contour lines of 90° and 270°, andsimilarly, 44 nm is also derived from the relation between the iso-phasecontour lines of 180° and 0°. Further, according to theiso-transmittance contour line in FIG. 4, it may be also appreciatedthat the reflectance of the first region 12 a is 0.38, and thereflectance of the second region 12 b is 0.36. Then, a result as shownin FIG. 25, for instance, is obtained from the calculation of the phasedifference and the reflectance ratio on the structure 2 by varying theMo film thickness of the second region 12 b inclusive of the multipleinterference effect in film in detail. From the illustrated result, itmaybe confirmed that the structure 2 shown in FIG. 24 is supposed to bein the form of the optimum constitution within the film thicknessadjustment range of each material.

Further, in the structure 2, the reflectance is 0.399 with respect tothe first region 12 a, and 0.396 with respect to the second region 12 b,in which case, the reflectance ratio therebetween results in 0.710%.Thus, the phase difference between the first region 12 a and the secondregion 12 b reaches 178.2° with respect to the TE wave and 178.3° withrespect to the TM wave.

The light intensity distribution in the case of the use of the Levensonphase shift mask of the above structure 2 is supposed to produce aresult as shown in FIG. 26, for instance, when the optical conditions ofNA=0.25 and σ=0.70 are applied to the case of the exposure of the waferto the light with the 120 nm-thick TaN absorption layer formed as wideas 40 nm (10 nm in terms of the wafer unit) on the four-fold mask of thestructure 2.

Further, 180° of the phase difference between the first region 12 a andthe second region 12 b may be confirmed by calculating the phasedifference according to the above expression (8) using the 320 nm-pitch(the 80 nm-pitch to the width of 10 nm in terms of the wafer unit)pattern with the TaN absorption layer having the width of 40 nm. FIG. 27shows a result of the calculation of the expression (8) on the positionright above the mask to the TEy wave, the TMx wave and the TMz wave.According to this illustration, both the TEy wave and the TMx wavesatisfactorily hold the phase difference of 180°. On the contrary, theTMz wave shows the more outstanding deviation from 180°, in which case,however, the contribution toward the transfer is as small as about0.45%, resulting in no effect on the transfer.

The deposition procedure of the structure 2 obtained after the settingof the complex refractive index and the film thickness as described theabove is approximately the same as that in the case of the abovestructure 1. The deposition procedure of the structure 2 is differentfrom that of the structure 1 in that the former procedure additionallyrequires, between the processes 5 and 6, a process of removing the Rulayer from the second region 12 b portion by the dry etching with Cl₂+O₂gas.

FIG. 28 is a schematic view showing a further different constitution ofthe Levenson phase shift mask. The illustrated structure (which will behereinafter referred to as “a structure 3”) is supposed to be onesatisfying the criteria 1 and 2 determined based on the iso-phasecontour line in FIG. 15 and the iso-reflectance contour line in FIG. 4,likewise the above structures 1 and 2. The first region 12 a has, on thereflective mask blank with multilayered films 11, the formative film inthe form of the multiple layers in the order of Ru of 5 nm, TaN of 20nm, Si of 8 nm and Ru of 5 nm. Further, the second region 12 b has theformative film in the form of the multiple layers in the order of Ru of5 nm, Si of 8 nm and Ru of 43.5 nm.

In the above structure 3, the Si is used as the composing material ofthe formative films of the first and the second regions 12 a and 12 b,unlike the case of the structure 1 or 2. The complex refractive index ofthe Si is 0.99932-0.00182645i whose real part is extremely close to 1specified as the refractive index in the vacuum and whose imaginary partis smaller than that of the other materials. Thus, the Si material isallowed to bear the role in the adjustment of the phase difference andthe reflectance ratio by taking advantage of the multiple interferenceeffect in film.

Thus, the constitution satisfying the criteria 1 and 2 may be obtainedfrom the iso-phase contour line in FIG. 15 and the iso-reflectancecontour line in FIG. 4 by taking a procedure of extracting a conditionfor preponderantly narrowing down the adjustment to the phase differencewithout taking the Si layer into consideration, and of then adjustingthe phase difference to reach close to 180°, while narrowing down theadjustment to the reflectance with the multiple interference effect infilm of the Si layer. That is, the constitution satisfying the criteria1 and 2 is supposed to be in the form of the multiple layers in theorder of Ru of 5 nm, TaN of 20 nm and Ru of 5 nm on the reflective maskblank with multilayered films 11 as for the first region 12 a, and inthe form of the multiple layers in the order of Ru of 5 nm and Ru of43.5 nm as for the second region 12 a. The first region 12 a in thiscase has the total film thickness of 30 nm, and shows the compositecomplex refractive index whose real part is 0.9234 and whose imaginarypart is 0.02687i. The second region 12 b has the total film thickness of48.5 nm, and shows the composite complex refractive index whose realpart is 0.8875 and whose imaginary part is 0.01747i.

With reference to the above structure 3, the calculation of thedifference in the level between the first region 12 a and the secondregion 12 b from the iso-phase contour line in FIG. 15 results in 22 nmof the above difference in the level based on the relation between theiso-phase contour lines of 90° and 27°, and similarly, 16 nm is derivedfrom the relation between the iso-phase contour lines of 180° and 0°.Further, according to the iso-transmittance contour line in FIG. 4, itmay be also appreciated that the reflectance of the first region 12 a is0.14 and the reflectance of the second region 12 b is 0.18. Then, aresult as shown in FIG. 29, for instance, is obtained from thecalculation of the phase difference and the reflectance ratio on thestructure 3 by varying the Mo film thickness of the second region 12 binclusive of the multiple interference effect in film in detail. Fromthe illustrated result, it may be confirmed that the structure 3 shownin FIG. 28 is supposed to be in the form of the optimum constitutionwithin the film thickness adjustment range of each material. Thestructure 3 employs the Si as the composing material of the formativefilms of the first and the second regions 12 a and 12 b, and also takesadvantage of the multiple interference effect in film obtained with theSi layer effectively, resulting in an attainment of the conditions underwhich the phase difference and the reflectance ratio satisfy thereference values.

Further, in the structure 3, the reflectance is 0.195 with respect tothe first region 12 a and 0.200 with respect to the second region 12 b,in which case, the reflectance ratio therebetween results in 2.41%.Thus, the phase difference between the first region 12 a and the secondregion 12 b reaches 185.3° with respect to the TE wave and 185.1° withrespect to the TM wave.

The light intensity distribution in the case of the use of the Levensonphase shift mask of the above structure 3 is supposed to produce aresult as shown in FIG. 30, for instance, when the optical conditions ofNA=0.25 and σ=0.70 are applied to the case of the exposure of the waferto the light with the 120 nm-thick TaN absorption layer formed as wideas 40 nm (10 nm in terms of the wafer unit) on the four-fold mask of thestructure 3.

Further, 180° of the phase difference between the first region 12 a andthe second region 12 b may be confirmed by calculating the phasedifference according to the above expression (8) using the 320 nm-pitch(the 80 nm-pitch to the width of 80 nm in terms of the wafer unit)pattern with the TaN absorption layer having the width of 40 nm. FIG. 31shows a result of the calculation of the above expression (8) on theposition right above the mask to the TEy wave, the TMx wave and the TMzwave. According to this illustration, both the TEy wave and the TMx wavesatisfactorily hold the phase difference of 180°. On the contrary, theTMz wave shows the more outstanding deviation from 180°, in which case,however, the contribution toward the transfer is as small as about0.45%, resulting in no effect on the transfer.

The deposition procedure of the structure 3 obtained after the settingof the complex refractive index and the film thickness as described theabove is also approximately the same as that in the case of the abovestructure 2. The procedure of the structure 3 is different from that ofthe structure 2 in that the process 8 in the former procedure requiresthe deposition of the Si layer and the Ru layer by the sputtering,instead of the Mo layer.

By the way, each of the structures 1 to 3 has the difference in thethickness of the formative film between the first and the second regions12 a and 12 b, resulting in the creation of the difference in the levelof the formative film between the first and the second regions. Theconstitution described the above is also supposed to enable the phaseshift effect to be obtained as described the above. However, with theconsiderations of the TaN absorption layer formed in the boundarybetween the first and the second regions 12 a and 12 b, it is morepreferable that the first and the second regions 12 a and 12 b areformed flat without having the difference in the level, in view of aneasiness in the fabrication. Thus, a specific instance of theconstitution in which both the first and the second regions 12 a and 12b are in the flat form is now described.

FIG. 32 is a schematic view showing a sectional structure of one flatconstitution of the Levenson phase shift mask. The illustrated structure(which will be hereinafter referred to as “a structure 4”) is supposedto be one satisfying the criteria 1 and 2 set based on the iso-phasecontour line in FIG. 15 and the iso-reflectance contour line in FIG. 4.The first region 12 a has, on the reflective mask blank withmultilayered films 11, the formative film in the form of the multiplelayers in the order of Ru of 3 nm, TaN of 7 nm, Ru of 6 nm, Si of 37 nmand Ru of 5 nm. Further, the second region 12 b has the formative filmin the form of the multiple layers in the order of Ru of 3 nm, Mo of 47nm and Ru of 8 nm.

In the above structure 4, the reason for the use of the Si for thecomposing material of the formative film of the first region 12 a is toallow the Si to bear the role in the adjustment of the phase differenceand the reflectance ratio by taking advantage of the multipleinterference effect in film, likewise the case of the structure 3. Thus,the constitution satisfying the criteria 1 and 2 may be obtained fromthe iso-phase contour line in FIG. 15 and the iso-reflectance contourline in FIG. 4 by taking the procedure of extracting the condition forpreponderantly narrowing down the adjustment to the phase differencewithout taking the Si layer into consideration and of then adjusting thephase difference to reach close to 180°, while narrowing down theadjustment to the reflectance with the multiple interference effect infilm of the Si layer. That is, the constitution satisfying the criteria1 and 2 is supposed to be in the form of the multiple layers in theorder of Ru of 3 nm, TaN of 7 nm, Ru of 6 nm and Ru of 5 nm on thereflective mask blank with multilayered films 11 as for the first region12 a, and in the form of the multiple layers in the order of Ru of 3 nm,Mo of 47 nm and Ru of 8 nm as for the second region 12 b. The firstregion 12 a in this case has the total film thickness of 21 nm, andshows the composite complex refractive index whose real part is 0.9054and whose imaginary part is 0. 03631i. The second region 12 b has thetotal film thickness of 58 nm, and shows the composite complexrefractive index whose real part is 0.9147 and whose imaginary part is0.000904i.

With reference to the above structure 4, the calculation of thedifference in the level between the first region 12 a and the secondregion 12 b from the iso-phase contour line in FIG. 15 results in 40 nmof the above difference in the level from the relation between theiso-phase contour lines of 90° and 270°, and similarly, 43 nm is derivedfrom the relation between the iso-phase contour lines of 180° and 0°.Further, according to the iso-transmittance contour line in FIG. 4, itmay be also appreciated that the reflectance of the first region 12 a is0.15 and the reflectance of the second region 12 b is 0.30.

As described the above, the above structure 4, although being supposedto be the same as the structures 1 and 2 without considerations of theSi layer, causes a disagreement in the reflectance between the firstregion 12 a and the second region 12 b. To eliminate the abovedisagreement, the structure 4 matches the reflectance in the firstregion 12 a and that in the second region 12 b by inserting the Si layerto take advantage of the multiple interference in film effectively.

Thus, the structure 4 requires that the constitution satisfying thecriteria 1 and 2 is obtained by appropriately varying the film thicknessof the TaN layer of the first region 12 a, the film thickness of the Molayer of the second region 12 b and the film thickness of the Si layerof the first region 12 b. FIG. 33 shows a result obtained from thecalculation of the phase difference and the reflectance ratio using thefilm thickness of the Mo layer as a parameter, with the film thicknessof the TaN layer and the film thickness of the Si layer fixed. From theillustrated result, it maybe confirmed that the structure 4 shown inFIG. 32 is supposed to be in the form of the constitution satisfying thecriteria, provided that the difference in the film thickness between thefirst region 12 a and the second region 12 b reaches 0 nm. The structure4 employs the Si as the composing material of the formative film of thefirst region 12 a, and takes advantage of the multiple interference infilm of the Si layer effectively, resulting in the attainment of theconstitution in which the phase difference and the reflectance ratiosatisfy the reference values and both the first region 12 a and thesecond region 12 b are in the flat form.

Further, in the structure 4, the reflectance is 0.285 with respect tothe first region 12 a and 0.287 with respect to the second region 12 b,in which case, the reflectance ratio therebetween results in 0.65%.Thus, the phase difference between the first region 12 a and the secondregion 12 b reaches 180.8° with respect to the TE wave, and 180.5° withrespect to the TM wave.

The light intensity distribution in the case of the use of the Levensonphase shift mask of the above structure 4 is supposed to produce aresult as shown in FIG. 34, for instance, when the optical conditions ofNA=0.25 and σ of 0.70 are applied to the case of the exposure of thewafer to the light with the 120 nm-thick TaN absorption layer formed aswide as 40 nm (10 nm in terms of the wafer unit) on the four-fold maskof the structure 4.

Further, 180° of the phase difference between the first region 12 a andthe second region 12 b may be confirmed by calculating the phasedifference according to the above expression (8) using the 320 nm-pitchpattern (the 80 nm-pitch to the width of 10 nm in terms of the waferunit) pattern with the TaN absorption layer having the width of 40 nm.FIG. 35 shows a result of the calculation of the expression (8) on theposition right above the mask to the TEy wave, the TMx wave and the TMzwave. According to this illustration, both the TEy wave and the TMx wavesatisfactorily hold the phase difference of 180°. On the contrary, theTMz wave shows the more outstanding deviation from 180°, in which case,however, the contribution toward the transfer is as small as about0.45%, resulting in no effect on the transfer.

The deposition procedure of the structure 4 obtained after the settingof the complex refractive index and the film thickness as described theabove may take, between the processes 5 and 6, a process of removing theRu layer from the second region 12 b portion by the dry etching with theCl₂+O₂ gas, likewise the case of the structure 2, and also requiresprocesses as shown in FIGS. 36 and 37 between the processes 13 and 14,in addition to the processes in the case of the above structure 1 (SeeFIGS. 20 to 23).

That is, as shown in FIG. 36, the deposition of the Ru layer in theprocess 13 is followed by the deposition of the Si layer by thesputtering (a process 13-1), and the coating of the resist furtherfollows (a process 13-2). Then, the removal of the resist from thesecond region 12 b portion is performed by way of the patterning and theresist development (a process 13-3).

Thereafter, as shown in FIG. 37, the Si film is removed from the secondregion 12 b portion by the dry etching with the Ar+Cl₂ gas (a process13-4). The Ru layer beneath the etched Si layer is supposed to functionas the etching stopper layer. Then, the separation of the resist (aprocess 13-5) and the deposition of the Ru layer by the sputtering (aprocess 13-6) are followed by the deposition of the TaN absorption layerby the sputtering (a process 14), and, thereafter, the processes similarto those in the case of the structure 1 follow. The above depositionprocedure enables the Levenson phase shift mask of the structure 4 to beconstituted.

As described the above, with reference to the structure 4, theconstitution satisfying the criteria 1 and 2 and having the first andthe second regions 12 a and 12 b in the flat form is specified byappropriately varying the film thickness of the TaN layer of the firstregion 12 a, the film thickness of the Mo layer of the second region 12b and the film thickness of the Si layer of the first region 12.However, the above constitution may be also obtained in the followingstructure.

FIG. 38 is a schematic view showing a sectional structure of a differentflat constitution of the Levenson phase shift mask. The illustratedstructure (which will be hereinafter referred to as “a structure 5”) isalso obtained as the result of the calculation of the phase differenceand the reflectance ratio using the film thickness of the Mo layer asthe parameter, with the film thickness of the TaN layer and the filmthickness of the Si layer fixed. FIG. 39 shows a result of thecalculation of the phase difference and the reflectance ratio with thefilm thickness of the Mo layer as the parameter, with the film thicknessof the TaN layer and the film thickness of the Si layer fixed. From theillustrated result, it maybe confirmed that the structure 5 is alsosupposed to be in the form of the constitution satisfying the criteria,provided that the difference in the film thickness between the firstregion 12 a and the second region 12 b reaches 0 nm. In the structure 5,the reflectance is 0.288 with respect to the first region 12 a, and0.287 with respect to the second region 12 b, in which case thereflectance ratio there between results in 0.36%. Further, the phasedifference between the first region 12 a and the second region 12 breaches 181.4° with respect to the TE wave and 181.1° with respect tothe TM wave.

The light intensity distribution in the case of the use of the Levensonphase shift mask of the structure 5 is supposed to produce a result asshown in FIG. 40, for instance, when the optical conditions of NA=0.25and σ=0.70 are applied to the case of the exposure of the wafer to thelight with the 120 nm-thick TaN absorption layer formed as wide as 40 nm(10 nm in terms of the wafer unit) on the four-fold mask of thestructure 5.

Further, 180° of the phase difference between the first region 12 a andthe second region 12 b may be confirmed by calculating the phasedifference according to the above expression (8) using the 320 nm-pitch(the 80 nm-pitch to the width of 10 nm in terms of the wafer unit)pattern with the TaN absorption layer having the width of 40 nm. FIG. 41shows a result of the calculation of the expression (8) on the positionright above the mask to the TEy wave, the TMx wave and the TMz wave.According to this illustration, both the TEy wave and the TMx wavesatisfactorily hold the phase difference of 180°. On the contrary, theTMz wave shows the more outstanding deviation from 180°, in which case,however, the contribution toward the transfer is as small as about0.45%, resulting in no effect on the transfer.

The deposition procedure of the above structure 5 is the same as that inthe case of the above structure 4.

FIG. 42 is a schematic view showing a sectional structure of a furtherdifferent flat constitution of the Levenson phase shift mask. Theillustrated structure (which will be hereinafter referred to as “astructure 6”) is also obtained as the result of the calculation of thephase difference and the reflectance ratio using the film thickness ofthe Mo layer as the parameter, with the film thickness of the TaN layerand the film thickness of the Mo layer fixed. FIG. 43 shows a result ofthe calculation of the phase difference and the reflectance ratio usingthe film thickness of the Mo layer as the parameter, with the filmthickness of the TaN layer and the film thickness of the Si layer fixed.From the illustrated result, it may be confirmed that the structure 6 issupposed to be in the form of the constitution satisfying the criteria,provided that the difference in the film thickness between the firstregion 12 a and the second region 12 b reaches 0 nm. In the structure 6,the reflectance is 0.300 with respect to the first region 12 a and 0.287with respect to the second region 12 b, in which case, the reflectanceratio therebetween results in 0.90%. Further, the phase differencebetween the first region 12 a and the second region 12 b reaches 180.6°,with respect to the TE wave and 180.3° with respect to the TM wave.

The light intensity distribution in the case of the use of the Levensonphase shift mask of the structure 6 is supposed to produce a result asshown in FIG. 44, for instance, when the optical conditions of NA=0.25and σ=0.70 are applied to the case of the exposure of the wafer to thelight with the 120 nm-thick TaN absorption layer formed as wide as 40 nm(10 nm in terms of the wafer unit) on the four-fold mask of thestructure 6.

Further, 180° of the phase difference between the first region 12 a andthe second region 12 b may be confirmed by calculating the phasedifference according to the above expression (8) using the 320 nm-pitch(the 80 nm-pitch to the width of 10 nm in terms of the wafer unit)pattern with the TaN absorption layer having the width of 40 nm. FIG. 45shows a result of the calculation of the expression (8) on the positionright above the mask to the TEy wave, the TMx wave and the TMz wave.According to this illustration, both the TEy wave and the TMx wavesatisfactorily hold the phase difference of 180°. On the contrary, theTMz wave shows the more outstanding deviation from 180°, in which case,however, the contribution toward the transfer is as small as about0.45%, resulting in no effect on the transfer.

The deposition procedure of the above structure 6 is also the same asthat in the case of the above structure 4 or 5.

An effect on the above Levenson phase shift mask is now described ascompared with that of the conventional binary mask that takes advantageof no phase shift effect. FIG. 46 illustrates the light intensitydistribution obtained under the optical conditions of NA=0.25 and σ=0.70in the case of the exposure of the wafer to the light with the 120nm-thick TaN absorption layer formed as wide as of 40 nm, 30 nm, 20 nm,10 nm and 0 nm (10 nm, 7,5 nm, 5 nm, 2.5 nm and 0 nm in terms of thewafer unit) on the four-fold mask of the structure 5 regarding theLevenson phase shift mask of the structure 5. According to thisillustration, it maybe appreciated that a satisfactory pattern contrastis obtained in each of the TaN absorption layer widths.

On the contrary, as for the conventional binary mask, FIG. 47illustrates the light intensity distribution obtained under the opticalconditions of NA=0.25 and σ=0.70 in the case of the exposure of thewafer to the light with the 120 nm-thick TaN absorption layer formed aswide as 40 nm, 30 nm, 20 nm, 10 nm and 0 nm (10 nm, 7.5 nm, 5 nm, 2.5 nmand 0 nm in terms of the wafer unit) on the above binary mask. Accordingto this illustration, it may be appreciated that the pattern contrastremarkably decreases with decreasing TaN absorption layer width.

For the above reasons, it may be said that the use of the Levenson phaseshift mask of the above structure may produce an outstanding effect ofpermitting the transfer of a line width of a size as small as 15 nm orbelow on the wafer in the case of the TaN absorption layer having thewidth of 10 nm (2.5 nm in terms of the wafer unit). Further, theexposure under the optical conditions of NA=0.30, as shown in FIG. 30,for instance, is supposed to produce the outstanding effect ofpermitting the transfer of the line width of a size as small as 10 nm orbelow on the wafer in the case of the TaN absorption layer having thewidth of 10 nm (2.5 nm in terms of the wafer unit).

As described the above, the phase shift mask having been described inthe embodiments (the first and the second embodiments) of the presentinvention requires that the film thickness and the complex refractiveindex of the formative films of the first region 12 a and the secondregion 12 b are set to ensure that the reflected light contained in theextreme ultraviolet radiation in the first and the second regionscreates the prescribed phase difference. More specifically, whenconstituting the phase shift mask, the phase and the reflectance of thereflected light based on the arbitrary complex refractive index and thearbitrary film thickness are firstly specified with reference to thearbitrary complex refractive index and the arbitrary film thicknesswithout depending on the formative films (the complex refractive indexin the composing material of the formative films) on the reflective maskblank with multilayered films 11, and the thickness and the complexrefractive index of the formative film in each of the first and thesecond regions are selected based on the specified phase and thespecified reflectance to ensure that the first region 12 a and thesecond region 12 b create the phase difference of 180°.

Thus, according to the phase shift mask having been described in theembodiments of the present invention, even in the case of the reflectivemask adapted to the extreme ultraviolet radiation, it becomes realizableto constitute the phase shift mask used for the resolution enhancedtechnology. That is, the use of the phase shift mask fabrication methodhaving been described in the embodiments of the present inventionenables the extreme ultraviolet phase shift mask to be constituted.

While the embodiments of the present invention have been described bytaking the case where the extreme ultraviolet radiation is used as theexposure light, it is to be understood that the exposure light is notlimited to the extreme ultraviolet light, and may be X-rays, radioactiverays, ultraviolet rays or a visible light. With the exposure lightsdescribed the above, it also becomes realizable to constitute the phaseshift mask used for the resolution enhanced technology for thereflective mask. That is, the use of the phase shift mask fabricationmethod having been described in the embodiments of the present inventionenables the extreme ultraviolet phase shift mask to be constituted.

Furthermore, according to the phase shift mask having been described inthe embodiments of the present invention, the use of not only theextreme ultraviolet radiation but also the resolution enhancedtechnology remarkably increases the pattern contrast on the wafer,resulting in the attainment of the resolution that has failed to beobtained with the conventional binary mask. That is, the semiconductorapparatus, if being fabricated using the phase shift mask according tothe embodiments of the present invention, may obtain moremicro-miniaturized hole patterns, space patterns and line patterns thanthose obtained with the conventional binary mask, resulting in a quitesuitable adaptation to the pattern minimization.

Furthermore, according to the phase shift mask having been described inthe embodiments of the present invention, the effective utilization ofthe multiple interference in film makes the formative film in the firstregion 12 a approximately equal in the film thickness with the formativefilm in the second region 12 b, resulting in the attainment of theconstitution in which the first region 12 a and the second region 12 bare in the flat form. Thus, even when the Levenson phase shift maskrequires the TaN absorption layer formed in the boundary between thefirst region 12 a and the second region 12 b, for instance, the TaNlayer maybe formed at a flat portion, resulting in an easiness inperforming the fabrication and also ensuring an accuracy in forming theabsorption layer.

Furthermore, according to the phase shift mask having been described inthe embodiments of the present invention, both or either of theformative films of the first and the second regions 12 a and 12 b hasthe multilayered structure consisting of the plurality of materials.Thus, the formative films that meet the arbitrary complex refractiveindex and the arbitrary film thickness may be obtained even byspecifying, with reference to the arbitrary complex refractive index andthe arbitrary film thickness, the phase and the reflectance of thereflected light based on the arbitrary complex refractive index and thearbitrary film thickness. That is, the use of the multilayered structureconsisting of the plurality of materials enables the desired phase shiftmask to be constituted.

As has been described the above, according to the exposure light phaseshift mask and the phase shift mask fabrication method according to thepresent invention, it becomes realizable to constitute the phase shiftmask for use in the resolution enhanced technology by obtaining anappropriate combination of the refractive index with the absorptioncoefficient, even in the case of the reflective mask adapted to theexposure light. Furthermore, according to the semiconductor apparatusfabrication method according to the present invention, the quitesuitable adaptation to the pattern minimization is attainable.

In particular, it becomes realizable to constitute the phase shift maskfor use in the resolution enhanced technology for the reflective maskrequired for the case where the extreme ultraviolet radiation is used asthe exposure light. That is, the use of the phase shift mask fabricationmethod having been described in the embodiments of the present inventionenables the extreme ultraviolet phase shift mask to be constituted.

1. A phase shift mask for an exposure light used to transfer a desiredpattern to a light exposed material by a reflection of the exposurelight, characterized by comprising: a reflective mask blank withmultilayered films that reflects the exposure light; and a first and asecond regions formed on the reflective mask blank with multilayeredfilms, wherein each film thickness and each complex refractive index ina formative film of the first region and a formative film of the secondregion are set to form a prescribed phase difference by a reflectedlight contained in the exposure light in the first region and areflected light contained in the exposure light in the second region. 2.The phase shift mask for an exposure light as cited in claim 1,characterized in that; said exposure light is one of an extremeultraviolet radiation, X-rays, radioactive rays, ultraviolet rays, and avisible light.
 3. The phase shift mask for an exposure light as cited inclaim 1, characterized in that; each film thickness and each complexrefractive index in a formative film of the first region and a formativefilm of the second region are set so that, in addition to the prescribedphase difference, a reflection rate of the reflected light contained inthe exposure light in the first region and a reflection rate of thereflected light contained in the exposure light in the second regionbecome approximately equal.
 4. The phase shift mask for an exposurelight as cited in claim 1, characterized in that; each film thickness inthe formative film of the first region and the formative film of thesecond region are configured to be approximately equal.
 5. The phaseshift mask for an exposure light as cited in claim 1, characterized inthat; one or both of the formative film of the first region and theformative film of the second region comprise a multilayer structureincluding a plurality of materials.
 6. The phase shift mask for anexposure light as cited in claim 3, characterized in that; each filmthickness and each complex refractive index in the formative film of thefirst region and the formative film of the second region are set usingan iso-phase contour line and an iso-reflectance contour line.
 7. Thephase shift mask for an exposure light as cited in claim 6,characterized in that; the iso-phase contour line is calculated byfixing an imaginary part of the complex refractive index.
 8. The phaseshift mask for an exposure light as cited in claim 1, characterized inthat; the phase shift mask is one of a halftone phase shift mask and aLevenson phase shift mask.
 9. A fabrication method of a phase shift maskfor an exposure light having a reflective mask blank with multilayeredfilms that reflects an exposure light, and a first and a second regionsformed on the reflective mask blank with multilayered films,characterized by: specifying, with reference to an arbitrary complexrefractive index to the exposure light and an arbitrary film thicknessof each film formed on the reflective mask blank with multilayeredfilms, a phase and a reflectance of a reflected light contained in theexposure light based on the above complex refractive index and the abovefilm thickness; and selecting, based on the specified phase and thespecified reflectance, each film thickness and each complex refractiveindex in a formative film of the first region and a formative film ofthe second region, so that the reflected light contained in the exposurelight in the first region and the reflected light contained in theexposure light in the second region form a prescribed phase difference.10. The phase shift mask for an exposure light as cited in claim 9,characterized in that; said exposure light is one of an extremeultraviolet radiation, X-rays, radioactive rays, ultraviolet rays, and avisible light.
 11. The fabrication method of a phase shift mask for anexposure light as cited in claim 9, characterized in that; when eachfilm thickness in the formative film of the first region and theformative film of the second region is selected, a phase difference dueto a multiple interference in film and a variation of reflection raterelative to the film thickness are considered.
 12. The fabricationmethod of a phase shift mask for an exposure light as cited in claim 9,characterized in that; the selected complex refractive index and thefilm thickness are calculated based on a composite complex refractiveindex performed by a multilayer structure made of a plurality ofmaterials, and a total film thickness.
 13. The fabrication method of aphase shift mask for an exposure light as cited in claim 9,characterized in that; each film thickness and each complex refractiveindex in the formative film of the first region and the formative filmof the second region are set using an iso-phase contour line and aniso-reflectance contour line.
 14. The fabrication method of a phaseshift mask for an exposure light as cited in claim 13, characterized inthat; the iso-phase contour line is calculated by fixing an imaginarypart of the complex refractive index.
 15. The fabrication method of aphase shift mask for an exposure light as cited in claim 9,characterized in that; the phase shift mask is one of a halftone phaseshift mask and a Levenson phase shift mask.
 16. A fabrication method ofa semiconductor apparatus including a lithography process oftransferring a desired pattern to a light exposed material using anexposure light phase shift mask, characterized by: specifying, withreference to an arbitrary complex refractive index to the exposure lightand an arbitrary film thickness of each film formed on a reflective maskblank with multilayered films, a phase and a reflectance of a reflectedlight contained in the exposure light based on the above complexrefractive index and the above film thickness; selecting, based on thespecified phase and the specified reflectance, each film thickness andeach complex refractive index in a formative film of the first regionand a formative film of the second region, so that the reflected lightcontained in the exposure light in the first region and the reflectedlight contained in the exposure light in the second region form aprescribed phase difference; forming the formative film of the firstregion and the formative film of the second region on the reflectivemask blank with multilayered films based on the selected complexrefractive index and the selected film thickness to constitute anexposure light phase shift mask having the first region and the secondregion on the reflective mask blank with multilayered films; andtransferring the desired pattern to the light exposed material using theresultant exposure light phase shift mask.
 17. The fabrication method ofa semiconductor apparatus as cited in claim 16, characterized in that;said exposure light is one of an extreme ultraviolet radiation, X-rays,radioactive rays, ultraviolet rays, and a visible light.
 18. Thefabrication method of a semiconductor apparatus as cited in claim 18,characterized in that; each film thickness and each complex refractiveindex in the formative film of the first region and the formative filmof the second region are set using an iso-phase contour line and aniso-reflectance contour line.
 19. The fabrication method of asemiconductor apparatus as cited in claim 18, characterized in that; theiso-phase contour line is calculated by fixing an imaginary part of thecomplex refractive index.
 20. The fabrication method of a semiconductorapparatus as cited in claim 16, characterized in that; the phase shiftmask is one of a halftone phase shift mask and a Levenson phase shiftmask.